1. Field of the Invention
This invention relates to processing silicone foam, and in particular, to a process for forming silicone foam into designated shapes of, but not limited to, low-density silicone foam.
2. Background Information
Conventional methods employed to mold silicone foam into large shapes encounter several problems. One such problem is the inability to form ("blow") silicone foam into large, thick shapes, while maintaining a uniform cell structure throughout the shape. Previous processes for molding shapes of various sizes and thickness included the use of "closed" molds. Closed molds require a porthole or vent system to allow the gases inside the mold to escape the mold. The gases were normally released as the material inside the closed mold cooled and set.
Prior applications that used a closed mold with silicone foam resulted in formed silicone foam shapes that would have air bubbles and disfigurations at the venting area, because the silicone foam as it cooled would attempt to expand through the venting area. Further, the layer adjacent to the inside of the closed mold had a high density due to the expanding layer being compressed against a non-expandable area, the closed mold. Prior applications would be limited in not being able to provide shaped articles having a low density, uniform cell structures of silicone foam.
A uniform cell structure is particularly important in non-skinned silicone foam molded pieces, because a uniform structure size provides uniform compressibility. Prior applications have also been unable to provide silicone foam shapes that simultaneously maintain a low density and have a good "skin" (outer surface). Either the outer skin of the formed silicone foam shape was fine and smooth without air bubbles, but easily torn and had an inner foam that was extremely dense, or the inner foam was low in density and the outer skin was pocked with air bubbles. For these reasons, to date, silicone foams have not been used to make large molded pieces.
For example, prior applications and methods have been unable to produce silicone foam shapes that could readily be used as chairs, seat cushions, or mannequins. Further, in closed environments, such as stores, shopping malls, airline cabins, or museums, it is desirable to use silicone foam instead of plastics because if a fire occurred, the gases produced by the combustion of presently available plastics or cushions can present a deadly hazard. For example, when ignited, polyurethane releases cyanide gas. Not only are these gases toxic, they are often corrosive. This corrosive characteristic can compromise the integrity of electronic systems in an enclosed environment. In non-enclosed and heavily populated environments the burning of cushions still presents a dangerous and damaging situation.
It has been discovered in accordance with the invention described below that a low density, lightweight, buoyant, fire-resistant, non-toxic, non-acidic and non-corrosive alternative to plastics or polyurethane is presently available through the molding of silicone foam. By molding silicone foam through a process disclosed below that includes an application method using an open air mold and a serpentine pouring or spraying application technique for applying a silicone foam mixture, and the use of a forced symmetrical inversion molding process, silicone foam can be formed to produce designated articles of various shapes and sizes. Also, by using the disclosed silicone foam molding process that includes a skinning operation, which includes the spraying or applying of pre-determined amounts of a silicone foam mixture into a detailed mold to produce an outer layer, and a bonding method, which includes the sealing and adhering of the outer layer to an inversion molded cut block of silicone foam to create a skinned molded piece, silicone foam can be formed to produce designated articles of various shapes and sizes having a low density, uniform cell structure with a smooth outer skin.